Crossing the Diplex Chasm to 85 MHz Author: Todd Gingrass Cable & Media Solutions
The DOCSIS 3.1 specifications have re-ignited the conversation about moving to 85 MHz and many operators are now starting to think about how to get there. Based on CCI Systems decades of industry experience, here s a guide for any cable operator that is considering such an upgrade. WHY 85 MHz? Address increasing competition from other providers The ever increasing demand for more bandwidth and services from subscribers are forcing operator networks to be in a near constant state of upgrade. By providing more upstream spectrum, providers can offer more upload bandwidth and additional symmetrical bandwidth products. A variety of factors, including the type of data connections used for popular video services like Netflix have made the amount of a subscriber s upstream bandwidth a gating factor for increasing downstream bandwidth. However, the jump to 85 MHz should not be underestimated or taken lightly. There are many factors that need to be considered, both business and technology related, that should play into your final decision and subsequent plan should you go forward. The most important thing to remember is that operators will have different reasons to proceed with an upgrade, while some will decide that it is not yet the right time. Either decision can be correct, as long as the proper analysis is done ahead of time. www.ccisystems.com 2 Know where you are today start with a basic assessment of your system All too often, operators are forced into making big decisions before gathering all of the critical information. This can be due to lack of time or overlooking the many upfront considerations. As an operator, you need to consider the marketing and sales perspectives and not view this as solely a technology decision. This will help you decide whether or not to engage in this kind of project. While it is important that you do not take on potentially expensive and time consuming projects without reward, you also want to make sure that they get done when needed. Missing the window for a critical upgrade can put a large dent in your sales and marketing efforts and can give the competition a big head start. Let s dive in and take a look at both sides.
3 SALES & MARKETING PERSPECTIVE Consider the network from the subscriber point-of-view Is a subscriber going to pay more on their bill so they can have an 85 MHz return path? Of course not! Most would not have a clue what a return path is, nor do they care about it. However, customers may pay for a higher tier of service. Higher tiers can be enabled when the proper upstream speeds can handle the heavy downstream speeds. Determining whether an upgrade is appropriate requires the answers to these questions: Are your customers actually asking for those higher speeds? Does your competition have higher speeds that you need to match? If the answer to these questions are no, then it may be best that you use the information in this paper to help plan this as a future project that you can roll into over a few years. If your answers are yes, this paper will help you understand how to proceed with an upgrade.
4 Consider the alteration to the network While the advantage in having an 85 MHz upstream comes in the form of the higher speeds, the disadvantage comes along the video side. This alteration forces the removal/moving of EIA channels 2-6. Make sure that a plan from a customer messaging perspective along with a technical solution accompany the upgrade. Make sure that a plan from a customer messaging perspective along with a technical solution accompany the upgrade. A final consideration is forecasting your data and video products and their associated take rate growth for the near to mid-range future. A few items to consider are: Growing your bandwidth packages per the individual and/ or increasing your data penetration rate will impact service groups and overall bandwidth needed Adding advanced hybrid video platforms for operators that can combine linear RF broadcast with over-the-top (OTT)/IP delivered video on demand (VoD) content to drive data speeds in the aggregate even though they are not always associated directly with the data package purchased by the subscriber Moving to a full IPTV over DOCSIS type of installation has an even greater effect The above items can have a combined effect no matter if they are delivered by DOCSIS only, DOCSIS Set-Top Gateway or a combination of the two. You will have to plan out the spectrum and increased load either way as it is all DOCSIS in the end. A reason for more upstream Make sure not to forget about the way that HTTP and TCP traffic works if you determine that more upstream is needed. Today s IP usage is dominated by traffic from adaptive bit rate streams like Netflix and YouTube. Since this traffic uses TCP, as downstream rates increase, the upstream continues to fill with a large amount of acknowledgments. Data packages should be at a minimum 10:1 ratio download:upload to accommodate for this. Thus a reason for more upstream bandwidth!
5 TECHNICAL PERSPECTIVE Take a healthy look at the current state of the network In order to get the full appreciation of what this project will entail, there will be a number of categories to consider: Outside plant electronics models (nodes and amps/line extender) Certain outside plant passives (return path conditioners, etc.) RF optics (both forward and return paths) Headend splitting and combining equipment models Cable Modem Termination System (CMTS) and modem models Digital headend and set-top box (STB) models Current and future planned channel line-up Current subscriber premise methodologies (splitters, filters, etc.) Let s start by working our way from the headend out to the subscriber. Look through the outside plant There are a number of areas that can drive how an operator will get to 85 MHz. The brand and vintage of the current amplifiers will greatly impact the overall cost of making this change. There are a few options to consider depending on what gear you currently have in place. Also, the design parameters of powering, levels and spacing need to be considered to employ the next options we discuss.
6 Once the vintage, bandwidth and design parameters are known, we can determine what our technical field options are. Everything from a complete upgrade to a more simplistic module swap are at our disposal to evaluate. If a network has not been upgraded in a long time, is sitting at 450 to 550 MHz and there is a demand for other forward services like many HD and DOCSIS channels, it may make sense for a complete upgrade. However, if you have gone or are going to an all-digital line up, those needs may not be as extreme. The alternative for a recently upgraded plant may be a module swap and rebalance. This option results in lower labor costs than the upgrade because it does not require resplicing. There are also a number of iterations in-between that may fit your unique situation. Different options for nodes and passives must also be looked at. Some nodes will be able to have a retrofitted module or a kit based swap and others may require larger alterations like complete change outs. Again, the less you need to resplice, the lower your overall costs will be. As for the passives, many operators may have put in return path conditioners for various reasons during past upgrades. These devices typically contain some type of diplex filter. The question is whether these devices will still be needed. If so, are there upgrade kits available for them or will they need to be completely changed out? Either way, do not forget about the devices. They have most likely been left alone since they were placed inside the network.
7 Explore the headend The headend is an interesting area to discuss for this application. Many critical items in the headend are often not realized and accounted for until much too late in the process. The main thing to remember is to always think through your entire signal flow from the absolute beginning to the absolute end and leave no area unaccounted for. We will start with the RF optics. This area is sometimes overlooked, as operators are so concerned about the RF outside plant electronics that they forget how it gets to and from the plant. Depending on what manufacturer and models you have in your system, you may be completely in the clear. The main thing to remember is to always think through your entire signal flow from the absolute beginning to the absolute end and leave no area unaccounted for. A traditional forward transmitter with a frequency range starting just above 50 MHz will typically be fine to stay in the system. This is because you will not be putting anything into EIA channels 2-6 and the diplex filter in the new node will filter out any unwanted noise. The return path, however, can hold some surprises. For quite some time, many return transmitters and receivers were capable of 5-200 MHz. However, there are some that are not. Also, over the past 10-15 years, many manufacturers created frequency stacking or digitizing type platforms. Many of these platforms were only rated to 42 MHz mainly due to the overall load on the transmitter. These platforms were very popular as they allowed for the use of a single fiber for the return transmission of multiple nodes or service groups. In addition, the digital nature of the signals often helped suppress some ingress. These systems need to be replaced with an updated 5-85 MHz or higher gear.
8 Now we will move on to the highly overlooked area of the combining and splitting network. Many operators look at these networks as places where they use only regular splitters and combiners. In many cases, they could be correct. However, you need to consider some elements that may be in the system, such as certain amplifiers with any existing diplex filters. These small items can cause a big hiccup during a cutover of services if they are not identified ahead of time. Having a good understanding of manufacturer roadmaps and timelines is key to making good decisions for many aspects of business. Next up is the CMTS and cable modems. The CMTS is one of the main reasons that you would be looking to perform an 85 MHz upgrade. However, the current CMTS you have may not be the one needed going forward. Many CMTS products, including ones that are DOCSIS 3.0, are not capable of 85 MHz in the upstream direction. Make sure that you understand your current platform and the roadmap to 85 MHz before you move forward with the entire plan. You do not want to be surprised having to potentially wait for product development in order to use a newly upgraded outside plant. The same goes for the cable modems/gateways. Having a good understanding of manufacturer roadmaps and timelines is key to making good decisions for many aspects of business.
9 Lastly, we need to talk about the digital headend control platform along with the easily overlooked area of STBs. As mentioned earlier, EIA channels 2-6 will need to move upwards in the spectrum. This can be handled in many ways. It may be a simple channel reassignment (if your programming contracts allow it) or perhaps you are going all-digital. Either way, there is a lot to think about in this area that is out if the scope of this discussion. The interesting aspect for this application is that the channel alterations need to happen prior to the upgrade, whereas in the past, you typically conducted an upgrade (mostly increasing forward spectrum) so that you could add more channels afterwards. Remember this during timeline planning because marketing will need ample time for subscriber changes. The interesting aspect for this application is that the channel alterations need to happen prior to the upgrade, whereas in the past, you typically conducted an upgrade so that you could add more channels afterwards. The somewhat hidden item in this mix is the downstream out-of-band (OOB) channel for STB communication. Many times, systems leave the OOB signals at the lower end of the specification (70-130 MHz). To get these platforms working once all of the diplex filters have been changed throughout the network, this frequency needs to be changed to a new, higher location within the specification one that all of the STBs in the field are compatible with. Creating a test plan for all models of STBs in your network and adding this to your timeline is yet another item to consider. Although it is a specification, you should still have a solid method of procedure for cutover that is thoroughly tested and receives positive results before proceeding. Maintenace Tip: Make sure to check the diplex filters in your test equipment.
10 Consider the customer premises This is an area where you only have so much control as an operator. We all know that as soon as the installer leaves the home, the subscriber may decide to alter the professional installation by adding or moving cables and splitters and changing the properties of the system inside the home. Knowing that this happens all too often, we have to consider that there will always be subscribers with sub-standard splitters and cabling in their homes. Manage adjacent device interference Also occurring on the customer premise is adjacent device interference. This is a major issue that can happen as an operator moves through the migration. It occurs when a transmitting device (new 85 MHz enabled cable modem) launches high amplitude (+45 dbmv) signal(s) that are above 50 MHz into the upstream. The result is the typical house splitter s port-toport isolation not being enough to stop the signal from hitting and saturating a legacy STB on its existing downstream receiver. Avoid this issue by considering it during the planning process. One way to mitigate adjacent device interference is with the use of filters. This problem typically will not have a significant impact between adjacent subscribers, as the drop cable and the tap plates should be enough to attenuate the signal. However, it is possible for some multi-dwelling unit type environments to encounter issues. This is another item that needs to be well thought out prior to starting the upgrade process as it can cause major logistical issues.
11 Adjacent Device Interference See below for a before and after diagram of adjacent device interference that shows the progression of potential signal flow after an 85 MHz plant upgrade is performed. The images illustrate an 85 MHz enabled modem that has upstream channels enabled in the 55-85 MHz range. It also depicts how a group of bonded +45 dbmv upstream channels can bridge the port-to-port isolation (avg. -28 db) of a typical house splitter and cause receiver saturation of a legacy STB. A. Typical house splitter with signal flow and levels B. Spectrum prior to 85 MHz upgrade and modem usage C. Spectrum from the cable modem perspective after 85 MHz upgrade and modem insertion D. Spectrum from the legacy STB perspective after 85 MHz upgrade and modem insertion. +17 dbmv bleed over signals from modem can be seen hitting the legacy STB.
12 LOOKING AHEAD Understand how to assess results and create your plan and budget Taking all of the prior items into account, an operator can see that this is a much bigger undertaking than just doing some work in the outside plant over the course of a month or two. There is a tremendous amount of assessment, testing, planning and coordinating between the technical and non-technical groups, along with any outside help that may be brought in. For complete planning and execution, it can easily be expected to take between 12-24 months for a project of this nature. A solid plan will have significant milestones that can be tracked and used to assess progress so that budget and time to new revenue stays on track. It is recommended that any operator looking to embark on this project talks to other operators that have been through the same process so that they can learn from real-world experiences. This is the type of project that can drain internal resources, so finding a trusted outside entity to assist filling gaps may also be needed. Build for the future with CCI Systems Gain the competitive edge and offer higher speeds to your subscribers by implementing an 85 MHz return path upgrade. Our advanced technical engineering staff can create a solution specific to your system. CCI Systems will help assess your system, uncover potential pitfalls and develop a budget-friendly upgrade plan that can help you to succeed in your market. Call us about an 85 MHz return path upgrade today. Contact 885-337-9299 info@ccisystems.com www.ccisystems.com